1. Field of the Invention
The invention relates to a torque detector.
2. Description of the Related Art
Japanese Patent Application Publication No. 2014-29304 (JP 2014-29304 A), Japanese Patent Application Publication No. 2013-160535 (JP 2013-160535 A), and Japanese Patent Application Publication No. 2015-31600 (JP 2015-31600 A) each describe an example of a torque detector provided with a magnetic shield. The torque detector includes an input shaft and an output shaft that are coaxially coupled to each other via a torsion bar, a permanent magnet fixed to the input shaft, a plurality of magnetic yokes fixed to the output shaft and disposed within a magnetic field of the permanent magnet to form a magnetic circuit, a pair of magnetic convergence rings configured to induce magnetic fluxes from the magnetic yokes, and a magnetic sensor configured to detect the magnetic fluxes induced by the magnetic convergence rings. The magnetic convergence rings respectively have protrusions disposed so as to face each other. The magnetic sensor is disposed between the protrusions. The magnetic shield is disposed so as to surround the magnetic convergence rings. The magnetic shield blocks external magnetic field noises that affect the torque detector, such as noises caused by turning on and off electric components mounted in a vehicle, noises caused by high-voltage power-transmission lines, and noises emanating from roads or surrounding buildings.
According to JP 2014-29304 A, JP 2013-160535 A, and JP 2015-31600 A, the magnetic shield having a C-shaped section is fitted onto a cylindrical holder provided with the magnetic convergence rings. According to JP 2014-29304 A, in order to fit the magnetic shield having a C-shape onto the cylindrical holder, bent portions provided at the opposite end portions of the magnetic shield are engaged into fitting grooves provided in an outer peripheral surface of the holder, with the distance between the opposite end portions of the magnetic shield increased against a spring force of the magnetic shield.
According to JP 2013-160535 A, in order to fit the magnetic shield having a C-shape onto the cylindrical holder, the distance between the opposite end portions of the magnetic shield is increased against a spring force of the magnetic shield, and the magnetic shield is fitted onto the holder, as in JP 2014-29304 A. Then, the opposite end portions of the magnetic shield are inserted, in a circumferential direction of the holder, into grooves provided in a pair of engagement portions of the holder. In this way, movement of the magnetic shield in the circumferential direction is prevented at the bottoms of the grooves.
In JP 2015-31600 A, the holder includes a pair of holder-halves having shapes obtained by splitting the holder into two pieces in the up-down direction. The holder-halves in a separated state are fitted into the magnetic shield having a C-shape from the respective axial end sides of the magnetic shield. Then, the opposite end portions of the magnetic shield are inserted into grooves provided in a pair of engagement portions of each of the holder-halves. In this way, movement of the magnetic shield in the circumferential direction in the holder is prevented at the bottoms of the grooves.
In JP 2014-29304 A and JP 2013-160535 A, in order to fit the magnetic shield having a C-shape onto the cylindrical holder, the distance between the opposite end portions of the magnetic shield is increased, and the magnetic shield is fitted to the holder with the distance between the opposite end portions of the magnetic shield increased. However, when the magnetic shield or the holder has a dimensional deviation, a backlash is caused after the magnetic shield is fitted to the holder.
With the technology described in JP 2015-31600 A, when the magnetic shield or the holder has a dimensional deviation, a backlash is caused after the magnetic shield is fitted to the holder, as in JP 2013-160535 A. In some cases, a magnetic shield is fastened to a holder with screws. However, fastening members, such as screws, are required. This increases the number of components, resulting in a cost increase.